1. Field of the Invention
The present invention relates to white light illumination device, and in particular to a phosphor wheel thereof.
2. Description of the Related Art
In a laser projector, a display light source is composed of a phosphor wheel collocated with a solid-state laser (serving as an excitation light source). The display light can be operated with high work, and its photoluminescence efficiency may largely enhance the electro-optical conversion and lumen output of the laser projector. Accordingly, the laser projector is the most important light source module of next-generation projection technologies of recent years. The conventional designs of the phosphor wheels in the laser projectors are divided into two main types: single region designs as shown in FIG. 1, and multi-region designs as shown in FIG. 2. In FIG. 1, one phosphor or a mixture of a plurality of phosphors is formed on all regions of a wheel-shaped substrate, e.g. a single phosphor region 10. In FIG. 2, phosphors of different colors are separately formed on different regions of a wheel-shaped substrate, e.g. a red phosphor region 2R, a yellow phosphor region 2Y, a green phosphor region 2G, and a blue phosphor region 2B.
The red light efficiency of the phosphor wheel is always the bottleneck of the light source lumen of the laser projector. The red phosphor has an inherently lower efficiency. Moreover, the red phosphor light output will be largely degraded by a high excitation laser watt due to thermal decay. In other words, the red phosphor efficiency not only shifts the D65 white balance of the projector, but also degrades total lumen of the projector. While the laser excitation of high watt is adopted, a yellow phosphor and/or an orange phosphor are usually collocated with a filter to get the desired red light. In the phosphor wheel with a single yellow phosphor region, the yellow phosphor is excited by a blue laser to form a yellow light. The yellow light can be split by a splitter into a green light and a red light, which are combined with the blue laser to serve as an image-forming light source, e.g. RGB light beams. However, the red light efficiency of this modification is still low (about 12 lm/W), thereby limiting the white light lumen efficiency (about 54.9 lm/W). Accordingly, expending the spectrum and efficiency of the red light region is always one of the major topics of the laser projectors.